Mann et al 2008: Korttajärvi

Larry Huldén writes:

The Finnish lake sediments can not be used for temperature interpretations in the 18th to 20th century unless you know exactly the history of the regional lake environment conditions. We have 180,000 lakes in Finland. It is very easy to cherry pick among them and say that it is a random sample. Of all lakes, 1,500 lakes are affected by lowering of water levels. These must be omitted. Many other are affected by agriculture including forestry. This affects the relative components of the sediments. This is well known although somebody can by chance use them for climate trends. Finnish prof. Matti Saarnisto has showed me graphs of lake sediments from Finland which can be used for temperature trends but still show strong deviations in the recent 200 years because of agriculture. These lakes are not always very close to agricultural sites.

In addition, we must remember that the fauna or flora in the sediments do not represent the temperature of the air because long term trends in water temperatures do not correlate with long term trends in air temperatures. I had a poster on this phenomenon in Italy in 2001 (or 2002?).

Larry Huldén
Finnish Museum of Natural History

Timo Hameranta writes:

Tiljander et al. discovered “an organic rich period from AD 980 to 1250” that they say “is chronologically comparable with the well-known ‘Medieval Warm Period’.” During this time interval, they report that “the sediment structure changes” and “less mineral material accumulates on the lake bottom than at any other time [our italics] in the 3000 years sequence analyzed and the sediment is quite organic rich (LOI ~20%).” From these observations they conclude that “the winter snow cover must have been negligible, if it existed at all [our italics], and spring floods must have been of considerably lower magnitude than during the instrumental period (since AD 1881),” which conditions they equate with a winter temperature approximately 2°C warmer than at present.

In support of this conclusion, Tiljander et al. cite much corroborative evidence. They note, for example, that “the relative lack of mineral matter accumulation and high proportion of organic material between AD 950 and 1200 was also noticed in two varved lakes in eastern Finland (Saarinen et al. 2001) as well as in varves of Lake Nautajarvi in central Finland c. AD 1000-1200 (Ojala, 2001).” They also note that “a study based on oak barrels, which were used to pay taxes in AD 1250-1300, indicates that oak forests grew 150 km north of their present distribution in SW Finland and this latitudinal extension implies a summer temperature 1-2°C higher than today (Hulden, 2001).” And they report that “a pollen reconstruction from northern Finland suggests that the July mean temperature was c. 0.8°C warmer than today during the Medieval Climate Anomaly (Seppa, 2001).”

I think I got those, mann[1061] – mann[1064], named as lightsum, darksum, thickness and xraydense. Interesting, those values look like they hit all time low values during the MWP, an indication of mild winters and less snow smelting in the spring time. On the 20th century they hit their all time high values, due to changes of the landscape and usage of the lake for waste water dumping.

During the nineteenth century, the seven sites experienced either general cooling or no trend in temperature. During the twentieth century, on the other hand, the authors report that “all sites show a warming trend during the first few decades of the century,” which peaks between 1930 and 1950. Thereafter, all of the sites again depict cooling, as well as a steep warming over the last ten to twenty years of the record. However, for only two of the seven sites does the final warming lead to warmer temperatures than those of the 1930s and 40s. Of the remaining five sites, three of them end up being cooler than they were prior to mid-century, while two of them end up exhibiting about the same temperature.

The authors caution:

“Overall for longer term studies of the Holocene, these results indicate the need to be cautious in the interpretation of proxy records, the importance of proxy method validation, the continuing need to use reinforcing multi-proxy approaches, and the need for careful site and method selection.”

“Few proxies can provide quantitative reconstructions of past continental climatic and hydrological changes. Here, we report the first alkenone-based reconstruction of late Holocene temperature and salinity changes in Lake Qinghai, China. The alkenone-temperature proxy (Uk′ 37) indicates up to a 1°C change in mean annual air temperature or a 2°C change in summer lake water temperature during the late Holocene. Oscillating warm and cold periods could be related to the 20th century warm period, the Little Ice Age, the Medieval Warm Period, the Dark Ages Cold Period, and the Roman Warm Period…”

“The paleoclimatic archive held in Lake Baikal sediments is of significant importance, given the lake’s position in one of the world’s most continental regions where there are few continuous, high quality records spanning the Quaternary….New robust radiocarbon chronologies for sediments deposited during the late glacial and Holocene in Lake Baikal allow detailed, multi-decadal records to be constructed for the last 14,000 years…”

5. Besonen, M.R., W. Patridge, R.S. Bradley, P. Francus, J.S. Stoner, and M.B. Abbott, 2008. A record of climate over the last millennium based on varved lake sediments from the Canadian High Arctic. The Holocene Vol.18,No 1, pp. 169-180, January 2008

“…the Lower Murray Lake varve thickness record suggests that summer temperatures in recent decades were among the warmest of the last millennium, comparable with conditions that last occurred in the early twelfth and late thirteenth centuries, but estimates based on the sediment accumulation rate do not show such a recent increase. The coldest conditions of the `Little Ice Age’ were experienced from ~AD 1700 to the mid-nineteenth century…”

“Temperature variations at Lake Qinghai, northeastern Qinghai–Tibet plateau, were reconstructed based on four high-resolution temperature indicators of the δ18O and the δ13C of the bulk carbonate, total carbonate content, and the detrended δ15N of the organic matter. There are four obvious cold intervals during the past 600 years at Lake Qinghai, namely 1430–1470, 1650–1715, 1770–1820, and 1920–1940, synchronous with those recorded in tree rings at the northeast Qinghai–Tibet plateau. The intervals of 1430–1470, 1650–1715, and 1770–1820 are consistent with the three coldest intervals of the Little Ice Age. These obvious cold intervals are also synchronous with the minimums of the sunspot numbers during the past 600 years, suggesting that solar activities may dominate temperature variations on decadal scales at the northeastern Qinghai–Tibet plateau.”

The four Tijlander sediment series are very powerful contributors to the Mann 2008 reconstruction. I’ve posted up a copy of the original study here. Take a look. Tiljander talks at length about a very pronounced MWP (citing, among other evidence, Hulden 2001) a point not mentioned by Larry Hulden in his comment, but notable.

We here at CA appreciate good comedy, but this is a good one. Try to find how Mann grabbed the wrong end of the stick here. Hint: the point is a bit subtle and does not hit you over the head, but once you see, it’s jawdropping.

After reading the Tiljander paper, it’s clear that the measurement of the amount of minerals deposited annually in the lake sedimentation (designated as LS by Tiljander) should be inverted if it is going to be used as a temperature proxy (which at one point in the paper Tiljander seems to caution against doing, suggesting instead that hydrology rather than temperature is indicated). According to the authors, in years where the temperature is colder, more snow falls in the winter and consequently the spring thaw brings a larger amount of erosion from the melting snow — depositing more minerals in the lake bottom.

This is in contrast to the measurement of the organic matter in the sedimentation (designated as DS by Tiljander). Again, according to the paper, in years where the temperature is warmer, more organic matter is deposited in the lake bottom. (Of course, the authors also point out that given the introduction of anthropogenic factors in recent times disturbing the natural deposition of sediment in the lake, neither of these relationships really holds true for the last two centuries)

Yet the proxy series used by Mann (Lightsum — proxy #1061) corresponding to the measurement of the minerals does not seem to be inverted. It appears to be used in the same fashion as the series for measurement of the organic matter (Darksum — proxy #1062). This seems like such an elementary mistake that I’m sure it must be me that is confused, and not Mr. Mann. Perhaps the Lightsum series was inverted by Mr. Mann without any clear notation?

There is practically no permafrost in Finland today and probably hasn’t been since the last glaciation. The exception is “palsar”, mounds of permanently frozen peat that occur locally in bogs in northernmost Finland. And while the southern limit of permafrost is very sensitive to climatic change, the deep permafrost in Northern Siberia is more durable than most people think. During the previous interglacial (which lasted for 10,000 years) temperatures were as much as 10 degrees higher than today on the Taimyr peninsula, and even so some permafrost survived (and no large CH4 outgassing occurred).

Mann’s flipping of the data is both humorous and illuminating. Yes, he used the data upside down (Upside-Down Mann) as a paleoclimate proxy based on a spurious correlation between increased sediments directly attributable to farming and a supposed teleconnection to world temperature. 🙂

I can’t believe it… Mann manages to bury his standards deeper and deeper, again and again. He should be in the Guiness book. This is just hilarious.

I’m sure it is just a mistake by Mann. But mistakes like this prove that whenever they get the “right” answer, no further research or data verification is performed. This way, errors can only bias any study in the desired direction. Bad science.

Re: Nylo (#13),
There is an additional irony here. The very same study was used by a Finnish TV program MOT in 2004 in order to support the idea of MWP (in Finland)! They even interviewed (script here) the third author (Antti Ojala) who estimated that MWP was 0.5C-1C warmer thant the present in Finland.

Mot: ”Mitä arvioisit, kuinka paljon lämpimämpää oli tuolloin keskiajalla Suomessa kuin on nyt?
[Mot: What would you estimate, how much warmer than the present it was during the medieval times in Finland?]

Ojala: ”Sitä on näiden perusteella aika vaikea täsmällisesti sanoa. mutta puhutaan tommosesta puolesta asteesta, jopa asteesta erilaisten eurooppalaisten tutkimusten valossa”.
[Ojala: In the light of these results, it is very hard to tell exactly, but we talk about something like half a degree, even one degree in the light of various European research results.]

It’s not converted directly into temperature. It’s standardized and then input into the Mannomatic RegEM algorithm, which we’re trying to figure out. At the end of the day, the Mannomatic will assign weights to these and other series and use that to make their temperature estimate. The $64 question is how much weight is borne by this sort of data in the final result. In the non-dendro recon, it appears to be quite material for their MWP estimates, but we don’t know yet.